Municipal agencies face a growing number of MS4 permit and watershed planning and compliance obligations. Many of these obligations require the quantification of expected runoff volumes and pollutant loads, as well as the runoff volume and pollutant load reductions estimated for planned or implemented BMPs.
For example, the 2013 California Phase II General MS4 Permit (MS4 Permit) specifically requires a Program Effectiveness Assessment and Improvement Plan (PEAIP) to include "quantification of pollutant loads and pollutant load reductions achieved by the program as a whole" (Section E.14.a.ii.a.6). The MS4 Permit Draft Attachment G includes a TMDL implementation requirement to provide "a quantifiable numeric analysis that uses published BMP pollutant removal estimates, performance estimates, modeling, best professional judgment, and/or other available tools to demonstrate that the BMP selected for implementation achieved the MS4's wasteload allocation". The California Storm Water Resource Plan Guidelines require "a metrics-based and integrated evaluation and analysis of multiple benefits". The Water Code Section 13383 Orders to Phase II MS4 Permittees requires a plan demonstrating that controls will achieve Full Capture System Equivalency of the trash generated from all Priority Land Uses (or equivalent alternative land uses).
In 2015, the County of Santa Barbara, and the Cities of Buellton, Solvang, Goleta, and Carpinteria (jurisdictions), along with Geosyntec Consultants (Geosyntec), developed a baseline pollutant load quantification, catchment prioritization, and BMP reduction model (LPR Model) to address these requirements. The LPR Model is accessible from an easy to use Excel interface and consists of five main components: 1) calculating the MS4 Permit Area and watershed baseline wet weather annual average pollutant load/runoff volume; 2) prioritizing catchments for program improvements; 3) tracking BMP implementation details (e.g., type of BMP implemented, catchment(s) implemented on, applicable land uses, etc.); 4) estimating the BMP pollutant load/runoff volume reductions; and 5) summarizing and formatting all results for easy reporting.
In this presentation we will describe recent enhancements that expand the capabilities to the LPR Model, including analysis and incorporation of new local land use monitoring data, determination of BMP capture estimates based on BMP design and local rainfall/runoff hydrology, ability to adjust runoff volumes based on the hydrologic connectivity of outfalls, and incorporation of maintenance condition into BMP performance estimates. Additionally, a module is currently under development to evaluate trash capture scenarios for both Track 1 and 2 and to demonstrate ongoing progress towards 100 percent compliance with the Trash Provision.
Then we will provide brief case studies of how the LPR Model is being implemented by MS4 permittees across the State to successfully and efficiently fulfill various but connected watershed planning and compliance obligations directly applicable to the audience, including 1) the quantification of multiple benefits (pollutant load reductions, groundwater recharge, and flood management benefits) for dozens of projects included in SWRPs; 2) tracking, quantification, and prioritization of public and private stormwater retrofit projects to meet MS4 Permit PEAIP requirements, 3) forecasting long-term BMP implementation needs to meet TMDL Waste Load Allocations (WLAs), and 4) demonstration of full trash capture based on a combination of existing and planned BMPs (as project progress allows). The audience will be invited to participate through a Q&A discussion specifying how the LPR model may be implemented to address their watershed specific planning and compliance obligations.